Radial venting axial fan for a power machine

ABSTRACT

A heat exchange system for a power machine that has an engine compartment and a heat exchanger compartment is discussed. The heat exchange system includes a fan housing located between the heat exchanger compartment and the engine compartment. A fan assembly that includes an axial fan and a radial fan coupled to a center shaft having a longitudinal axis extending through the center shaft is positioned within the fan housing. The fan assembly is operably coupled to a fan drive mechanism that is configured to cause the fan assembly to rotate about the longitudinal axis in a first direction and a second direction. First and second control signals from a controller cause the drive mechanism to rotate in the first and second directions, respectively.

BACKGROUND

The present disclosure is related to power machines. More particularly, the present disclosure is related to systems and methods for cooling power machine related components and fluids. Power machines often utilize internal combustion engines, which provide power to propel machines. In addition, internal combustion engines can provide power to systems that are configured to provide other functions for the power machines. For example, some power machines include hydraulic systems, which are capable of receiving power from a source such as the internal combustion engine and convert that power into a useable form to accomplish work tasks.

Power systems such as internal combustion engines and hydraulic power supplies generate a large amount of heat during operation. Therefore, it is desirable to provide various cooling apparatuses to remove heat from power systems to maintain a temperature within the power system at which the power system operates efficiently without subjecting the power system to potential heat related damage.

SUMMARY

In one illustrative embodiment, a heat exchange system for a power machine having an engine compartment and a heat exchanger compartment is discussed. The heat exchange system illustratively includes a fan housing located between the heat exchanger compartment and the engine compartment. A fan assembly having an axial fan and a radial fan coupled to a center shaft is positioned within the fan housing. The fan assembly has a longitudinal axis that extends lengthwise through the center shaft. A fan drive mechanism is operably coupled to the fan assembly. The fan drive mechanism is configured to cause the fan assembly to rotate about the longitudinal axis in a first direction and a second direction. A controller is operably coupled to the fan drive mechanism. The controller is configured to provide a first control signal to the fan drive mechanism to cause the fan drive mechanism to rotate in the first direction and a second control signal to the fan drive mechanism to cause the fan drive mechanism to rotate in the second direction.

In another illustrative embodiment, a power machine having an engine located in an engine compartment and a heat exchanger located in a heat exchanger compartment is discussed. The power machine includes a fan housing with a fan assembly located within the housing. The fan housing is positioned between the engine compartment and the heat exchanger compartment. The fan assembly is configured to rotate in a first direction and a second direction. The power machine further includes a sensor configured to provide a sensor signal indicative of an operational condition and a fan override device capable of being manipulated by the operator. The fan override device is configured to provide an override signal that is indicative of its status. A controller is operably coupled to the fan assembly and configured to receive the sensor signal and the fan override signal. The controller is configured to control rotation of the fan assembly based on the sensor signal and the operator signal.

In yet another illustrative embodiment, a method of exchanging heat in a power machine is discussed. The method includes the step of providing a fan housing between an engine compartment and a heat exchanger compartment. The fan housing include a fan assembly located therein with an axial fan operably coupled to a radial fan. The fan assembly is capable of being rotated in two different directions. The method further includes receiving a first input signal that is indicative of the status of a fan override input and a second input signal indicative of the status of an operating condition of the power machine. The rotation of the fan assembly is controlled in response to the first and second input signals.

This Summary is provided to introduce a selection of concepts in a simplified form that are further discussed below in the Detailed Description. This Summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used as an aid in determining the scope of the claimed subject matter.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side elevation view of a power machine in which a cooling fan having a control system or method of the type discussed herein may be useful.

FIG. 2 is a block diagram illustrating a cooling system for a power machine according to one illustrative embodiment.

FIGS. 3-4 provide perspective views of the cooling system of FIG. 2.

FIG. 5 is a bottom view of the cooling system of FIG. 3.

FIG. 6 is a cutaway view of the cooling system of FIG. 3, illustrating a dual cooling fan arrangement located within a fan housing.

FIG. 7 is a block diagram illustrating a fan drive system for controlling the cooling fan of FIG. 6.

FIG. 8 is a flow diagram illustrating a method of controlling the cooling fan of FIG. 6.

DETAILED DESCRIPTION

FIG. 1 illustrates a power machine 10 in which a cooling fan and a fan control system or method of the type discussed herein may be useful. The illustrative power machine 10 of FIG. 1 includes a frame 12 that is supported by wheels 14. Frame 12 includes a pair of uprights 36 (only one is shown) disposed on either side of the power machine 10. The engine of power machine 10 supplies power to the wheels 14 causing the power machine to move under the control of an operator. Frame 12 supports a cab 16, which defines an operating compartment. An operator can be positioned inside the cab 16 and control the power machine 10.

End gate 32 is pivotally attached to the frame 12 along one of the uprights 36 and is removably attached to the other upright 36 at a latch (not shown). When the end gate 32 is not attached to the upright 36 at the latch, end gate 32 can be opened to allow access to an engine compartment 40, which is positioned between the uprights 36 and accepts an engine (not shown in FIG. 1) located therein. In addition, a heat exchanger compartment 42 is located above the engine compartment 40. A louvered aperture 34 positioned between the upright 36 and the cab 16 provides an outlet for airflow in or out of the heat exchanger compartment 42. A general arrangement of the heat exchanger compartment 42 and the engine compartment 40 is discussed in U.S. Pat. No. 4,815,550 of Mather et al., assigned to Clark Equipment Company, which is hereby incorporated by reference in its entirety. It will be appreciated that other arrangements and positioning of the heat exchanger compartment 42 and the engine compartment 40 can be incorporated without departing from the spirit and scope of the invention.

Power machine 10 further includes a lift arm 18, which is coupled to the frame 12 at a pivot point 26 located on upright 36. Lift actuator 20 is coupled to the frame 12 at first pivot point 22 and the lift arm 18 at second pivot point 24. A single lift arm 18 is shown in FIG. 1, but it is to be understood that a similar lift arm and corresponding actuator may be positioned on the opposite side of the cab and similarly attached to the frame 12. Further, it should be understood that such a lift arm may be coupled to the lift arm 18 shown in FIG. 1 via a cross-member (not shown) that extends between and is attached to each of the lift arms 18.

In one illustrative embodiment, lift actuators 20 are hydraulic cylinders. Thus, the power machine 10 illustratively includes a hydraulic power supply such as a hydraulic pump (not shown in FIG. 1), which is coupled to the engine and supplies a flow of pressurized hydraulic fluid to the lift actuators 20 to cause the lift arms 18 to be raised and lowered. Further, an attachment interface 28 is illustratively shown as being rotatably coupled to the lift arms 18 at an attachment point 30. One or more tilt actuators (not shown) are coupled to the attachment interface 28 and the one or more lift arms 18 (or the cross-member that extends between the lift arms 18). The one or more tilt actuators are illustratively operatively coupled to the hydraulic pump. By supplying hydraulic oil to the one or more tilt actuators, the tilt actuators can extend or retract, causing the attachment interface to pivot about the attachment point 30 in a direction illustrated by arrow 38.

In addition, the power machine 10, in one illustrative embodiment, employs a hydraulically powered drive system (not shown in FIG. 1). The hydraulically powered drive system is coupled to the engine to receive a power output from the engine and convert that power to a drive mechanism that, in turn, supplies power to the wheels 14, thereby causing wheels 14 to move and propel the power machine 10.

FIG. 2 is a block diagram of a portion of power machine 10, illustrating a heat exchanger system 50 utilized therein according to one illustrative embodiment. As is discussed above and is illustrated in FIG. 2, power machine 10 includes an engine 52. Engine 52 provides power for a number of different functions and components within the power machine 10, some of which will be discussed in more detail below. Due to the large amount of heat generated by the engine 52 during operation, it is useful to remove heat from the engine 52 to assist in maintaining an efficient operating temperature and to reduce the likelihood of heat-related damage to the engine 52.

One method of removing heat from the engine 52 is to circulate a cooling liquid through the engine 52 to remove heat from the engine 52 and thereby maintain a desired temperature within the engine. The cooling liquid can also be circulated through a heat exchanger or radiator 56, which removes heat from the cooling liquid. The cooling liquid, in one illustrative embodiment, is circulated from the engine 52 to the radiator 56 and back through the engine 52 through conduits 54. The conduits 54 shown in FIG. 2 are for illustrative purposes only and it is to be understood that any configuration of conduits 54 between the engine 52 and the radiator 56 may be employed in power machine 10 without departing from the spirit and scope of the discussion.

In one illustrative embodiment, the engine 52 is coupled to a hydraulic pump 58 and one or more hydraulic or hydrostatic drive pumps 60, each of which receives power from the engine 52 and provides a flow of pressurized hydraulic oil to various hydraulic and/or hydrostatic components on the power machine 10. For example, the hydraulic pump receives oil at an inlet 64 from, for example, a sump 62. The pump 58 then illustratively pumps oil from an outlet 66 through conduits 80 to the actuators 20. The hydraulic oil received at the actuators 20 causes the actuators 20 to move, which causes the lift arms 18 to be raised or lowered.

It should be understood that the block diagram of FIG. 2 is provided for illustrative purposes only and does not describe a hydraulic circuit in detail. For example, a control value (not shown) may be positioned between the outlet 66 of the hydraulic pump 58 and the lift actuators 20 to control the rate and direction of flow of hydraulic oil from the hydraulic pump 58 to the lift actuators 20. In addition, oil can be ported through the control valve to other components such as, for example, the tilt actuators discussed above.

Similarly, the drive pump 60 illustratively provides a flow of pressurized hydraulic oil that it receives at inlet 68 from sump 62 though outlet 70 to one or more drive motors 72 via conduits 82. The one or more drive motors 72 are each operatively coupled to one or more wheels 14 and provide a force to cause the one or more wheels 14 to move. Although only one drive pump 60 is shown in FIG. 2, power machine 10 can have more than one drive pump 60, each of which provides a flow of pressurized hydraulic oil to one or more drive motors 72, without departing from the spirit and scope of the discussion.

Hydraulic oil that is pumped through the hydraulic components described above, in addition to providing fluid power, absorbs heat from, and thus provides cooling to, the hydraulic components including the pumps, motors, valves, and actuators described above. In one illustrative embodiment, the hydraulic oil also circulates through a heat exchanger in the form of an oil cooler 74, which removes heat from the hydraulic oil in a manner similar to the radiator 56. Hydraulic oil is illustratively shown as being provided to the oil cooler 74 from motor 72, actuator 20, hydraulic pump 58, and drive pump 60 via conduit 84. Once the hydraulic oil traverses the oil cooler 74, it is illustratively returned to sump 62. However, any variations in the arrangement of components and porting of hydraulic oil within power machine 10 can be made without departing from the scope and spirit of the discussion.

For illustrative purposes, the oil cooler 74 and radiator 56 are considered to be part of the heat exchanger system 50 of power machine 10. Of course, the fluids that circulate through the oil cooler 74 and radiator 56 provide cooling to hydraulic and engine components and are understood to be part of a liquid cooling system that includes heat exchanger system 50.

Heat exchanger system 50, in one illustrative embodiment, also includes a fan assembly 76. Fan assembly 76 causes air to flow across surfaces of the oil cooler 74 and the radiator 56, to remove heat that has been absorbed from the fluids that flow through the oil cooler 74 and the radiator 56. A fan drive 78 is coupled to the fan assembly 76. Fan drive 78, in one illustrative embodiment, provides power to fan assembly 76 and controls the rate and direction of rotation of fan assembly 76. Fan assembly 76 can draw air across the oil cooler 74 and radiator 56, or alternatively, can force air across the oil cooler 74 and radiator 56. The nature and operation of the fan assembly 76 and the fan drive 78 will be discussed in more detail below.

The power machine 10 shown in FIG. 1 is a skid steer loader. However, it should be appreciated that the cooling systems and methods discussed below may be useful in a number of different types of power machines. For example, the power machine 10 can be an excavator, wheeled or tracked loader, utility vehicle, all-wheel steer loader, tractor, or any other power machine. Thus, the concepts discussed within this document should not be limited to any one particular type of power machine.

FIGS. 3-6 illustrate the components of the heat exchanger system 50 configured for installation into power machine 10 according to one illustrative embodiment of the invention. As discussed above, heat exchanger system 50 includes a radiator 56 and an oil cooler 74, each of which is located in a heat exchanger compartment 42 located between uprights 36 of the power machine 10. The radiator 56 is configured to receive and allow engine coolant to flow through the radiator 56. Oil cooler 74 is configured to accept and allow hydraulic oil to flow through it.

A fan housing 120 is positioned between the engine compartment 40 and the heat exchanger 42 compartment within the power machine 10. The fan housing 120 has an aperture 122 that is positioned adjacent a second side 118 of radiator 56. In addition, the fan housing 120 has an aperture 124 that is oppositely positioned from aperture 122. Aperture 124 is positioned to allow air to flow between the fan housing 120 and the engine compartment. In one illustrative embodiment, the aperture 124 has a mesh pattern 126 that subdivides the aperture 124 into a plurality of smaller apertures. Fan housing 120 is shaped so that apertures 128 are positioned adjacent to louvered apertures 34 to allow air to flow between the fan housing 120 and outside the power machine 10.

Fan assembly 76 is positioned within the fan housing 120. Fan assembly 76 includes an axial fan 132, which includes a plurality of axial fan blades extending from the center shaft 134. The axial fan 132 is positioned adjacent the aperture 122 that is in turn positioned adjacent the heat exchanger compartment 42. Fan assembly 76 also includes a radial fan 136, which includes a plurality of radial fan blades coupled to the center shaft 134. The radial fan 136 is positioned adjacent aperture 124, which, in turn, is positioned to allow airflow between the fan housing 120 and the engine compartment 40.

In one illustrative embodiment, the center shaft 134, to which both the axial fan 132 and the radial fan 136 are attached, is coupled to a fan drive mechanism 138. The fan drive mechanism 138 is configured to rotate the center shaft 134 and, by extension cause the axial fan 132 and the radial fan 136 to rotate. Fan drive mechanism 138 is, in the illustrative embodiment, a hydraulic motor, which is powered by a hydraulic pump. Alternatively, the fan drive mechanism 138 can be any type of motor or drive mechanism.

In one illustrative embodiment, the fan drive mechanism 138 is capable of rotating and thereby causing the center shaft 134 to rotate in one of two directions. When the fan drive mechanism 138 rotates in a first direction, the axial fan 132 draws air into the fan housing from the heat exchanger compartment. As a result, air is drawn into the heat exchanger compartment 42 and past the oil cooler 74 and the radiator 56, thereby drawing heat away from the oil cooler 74 and radiator 56. Once the air is drawn through the heat exchanger compartment and into the fan housing 120, it is forced out of the housing through the apertures 128 and the louvered apertures 34.

Similarly, when the fan drive 138 rotates in the first direction, the radial fan 136 rotates so as to draw air through the engine compartment 40, thereby drawing heat out of the engine compartment 40. The resultant air is also forced out of the louvered apertures 34. When the fan drive 138 rotates in a second direction that is opposite the first direction, air is drawn in through the louvered apertures 34 and forced out through the apertures 122 and 124 into the engine and the heat exchanger compartments 40 and 42.

As discussed above, the fan drive 78 controls the rate and direction of rotation of fan assembly 76 as well as providing power to fan assembly 76. Fan drive mechanism 138, in one illustrative embodiment, provides a portion of the fan drive 78, which is illustrated in a block diagram in FIG. 7. Fan drive 78 illustratively includes a controller 140. Controller 140 can be any type of electrical device suitable for performing the functions discussed herein. In one illustrative embodiment, controller 140 includes a micro-controller integrated circuit that is capable of executing a series of instructions.

Controller 140 receives input signals from one or more sensing elements and one or more operator inputs. In one illustrative embodiment, the controller 140 receives input signals from an engine coolant temperature sensor 142 and a hydraulic oil temperature sensor 144 indicative of the temperatures of the engine coolant and hydraulic oil, respectively. In addition, the controller receives an input signal from a fan control override device 146. Based on the status of the signals provided by the sensors 142 and 144 and the fan control override device 146, the controller 140 can provide control signals to a directional control device 148. The relationship between the input signals and the direction control device 148 will discussed in more detail below.

Directional control device 148, in one illustrative embodiment, is a hydraulic control valve. The direction control device 148 is coupled to a hydraulic pump 150 at an inlet 154. Pump 150 draws hydraulic oil from sump 62 and pumps the oil into the directional control device 148. Oil is returned from the directional control device 148 to sump 62 through outlet 156. Directional control device 148 has an “A” port and a “B” port, which are coupled to “A” and “B” ports, respectively, on fan drive mechanism 138, which, in the illustrative embodiment, is a hydraulic motor. Hydraulic oil is ported from the directional control device 148 to the fan drive mechanism 138. Depending upon the direction that the oil is ported, the fan drive mechanism 138, will cause an output shaft 158 to rotate in one of two directions. Output shaft 158 is fixedly coupled to the center shaft 134 of the fan assembly 76. Thus, the fan drive mechanism 138 causes the fan assembly 76 to rotate.

Directional control device 148, as illustrated has a three-position valve 170, although it should be appreciated that the directional control device 148 can have variable positions. Controller 140 is coupled to a pair of actuators 160 and 162. Controller 140 is configured to provide a first control signal 164 to actuator 160 and a second control signal 166 to actuator 162. When controller 140 provides neither the first control signal 164 nor the second control signal 166, the Y position is presented to ports A and B as well as inlet 154 and outlet 156. As a result, hydraulic oil is not able to flow from the pump 150 to the fan drive mechanism 138. Instead, the oil is ported back to the sump 62 through outlet 156. Thus, when no control signal is provided by the controller 140, fan assembly 76 is not driven by the fan drive mechanism 138. Alternatively, the hydraulic oil flow provided at inlet 154 can be blocked in the Y position. This may require a pressure relief port. The valve 170 shown in FIG. 7 illustrates functionality related to providing oil flow to the fan drive mechanism 138. It should be appreciated that valve 170 and other hydraulic components shown in FIG. 7 can include other features such as relief valves or ports that are not illustrated in FIG. 7.

When controller 140 provides a first control signal 164 to actuator 160, actuator 160 causes valve 170 to shift. Thus, the X position is presented to ports A and B as well as inlet 154 and outlet 156. In this instance, hydraulic oil is provided from the pump 150, through the A port of the valve 170 to the A port of the fan drive mechanism 138. Hydraulic oil returns from the fan drive mechanism 138 via its B port to the B port of the valve 170 and to the sump 62. This causes the output shaft 158 to rotate in the first direction.

Conversely, when controller 140 provides a second control signal 166 to actuator 162, actuator 162 causes valve 170 to shift. Thus, the Z position is presented to ports A and B as well as inlet 154 and outlet 156. In this instance, hydraulic oil is provided from the pump 150 through the B port of the valve 170 to the B port of the fan drive mechanism 138. Hydraulic oil returns from the fan drive mechanism 138 via its A port to the A port of the valve 170 and to the sump 62. This causes the output shaft 158 to rotate in the second direction.

The discussion of directional control device 148 is for illustrative purposes only and is not meant to be limiting. It should be recognized that any configuration of directional control device 148 and fan drive mechanism 138 can be used without departing from the scope of the invention. For example, any type of hydraulic valve can be used as a directional control device. In addition, the actuators 160 and 162 may receive control signals that cause the value to move only a portion of its full travel, thereby controlling the amount of flow of hydraulic oil to the fan drive mechanism 138 and therefore controlling the speed of rotation of the fan 76. As another example, fan drive mechanism 138 can be an electric motor and directional control device 148 an electrical bridge configured to direct electrical signals to such an electrical motor.

FIG. 8 is a flowchart that illustrates a method 200 of controlling the fan assembly 76 according to one illustrative embodiment. Beginning at block 202, the status of the fan control override device 146 is determined. In one illustrative embodiment, the fan control override device 146 has two states, active and not active. The signal received from the fan control override device 146 indicates whether the fan control override device 146 is active. If the fan control override device 146 is active, determined at decision block 204, the controller 140 determines that the fan assembly 76 should rotate in an appropriate direction to force air out of the fan housing 120 and into the engine compartment and the heat exchanger compartment. This is represented at block 206.

If it is determined at block 204 that the fan control override device 146 is not active, the controller 140 considers the status of the sensing elements to determine a fan control stage. First, the sensor values for sensors 142 and 144 are obtained. This is represented at block 208. The fan control stage can be one of three stages: one, two, or three. The fan control stages are based on the values provided by the sensors 142 and 144. If the sensors 142 and 144 provide temperatures below a certain level, it is not useful to cause fan assembly 76 to rotate. This is stage one. The controller 140 thus determines whether the values from sensors 142 and 144 are such that the fan control is at stage one, as is represented by block 210. If it is determined that the fan control is at stage one, the valve 170 is positioned at the Y position, thereby preventing oil from flowing to the fan drive mechanism 138. This is represented in block 212.

If it is determined that the fan control is not at stage one, the controller 140 next determines whether the fan control is at stage two. This is represented by decision block 214. At stage two, the fan assembly 76 is driven in an appropriate direction so that it draws air from the engine compartment 40 and the heat exchanger compartment 42. If the controller 140 determines that the fan control is at stage two, the fan assembly 76 is set to draw air. That is, the fan assembly 76 is driven in the appropriate direction. This is illustrated by block 216.

If it is determined that the fan control is not at stage two, then, by default, the fan control is at stage three. At stage three, the temperature sensors 142 and 144 have determined that the temperature is high enough that potentially there is excessive debris located in the engine and/or heat exchanger compartments. The controller 140 will thus send the appropriate signal to the directional control device 148 to cause the fan drive mechanism 138 to rotated in an appropriate direction to force air into the engine and heat exchanger compartments 40 and 42 for a predetermined amount of time in an attempt to clear out the compartments. Thus, the controller 140, having determined that the fan control is at stage three, first determines whether the appropriate signal has been sent to the directional control device 148 to force air out of the fan housing 120 and into the engine and heat exchanger compartments 40 and 42. This is indicated by decision block 218. If the appropriate signal has not been sent to the directional control device 148, a timer is initialized, as is indicated by block 220 and the appropriate signal is sent to the directional control device 148. Thus, the fan is set to force air into the engine and heat exchanger compartments 40 and 42, as is indicated by block 206.

Returning to block 218, if the fan has been previously set to force air into the engine and heat exchanger compartments, the timer is then checked to determine whether the predetermined amount of time has elapsed. This is represented by block 222. If the timer has reached the maximum or predetermined time, the fan is set to draw air from the engine and heat exchanger compartments 40 and 42. This is represented by block 216.

In one illustrative embodiment, the fan control can reach stage three only once per run cycle of the power machine 10. Alternatively, the fan control can reach stage three repeatedly throughout a run cycle, with or without a delay to require that a certain amount of time pass before the fan control enters stage three again. In yet another illustrative embodiment, an input from an operator can prevent the fan control from ever reaching stage three, regardless of whether the temperatures from the sensors 142 and 144 would otherwise indicate that stage three fan control is warranted. It should be understood that the flowchart 200 is directed only to determining fan directional control. In addition, the controller 140 can control the speed of the fan 76 based on the readings that it receives from the sensors 142 and 144 and any other inputs that may be received by the controller 140.

The embodiments discussed above provide important advantages. A fan is discussed that is configured to alternatively draw air from both an engine compartment and a heat exchanger compartment into the fan housing simultaneously or force air out from the fan housing into the engine compartment and heat exchanger compartment simultaneously. The directional control can be manually or automatically controlled. Such embodiments provide for improved cooling capability in a power machine by including, for example, a way to force debris out of compartments that might otherwise inhibit the ability of a cooling system to maintain efficient temperature levels within the engine and hydraulic systems of the power machine.

Although the present invention has been described with reference to preferred embodiments, workers skilled in the art will recognize that changes may be made in form and detail without departing from the spirit and scope of the invention. 

1. A heat exchange system for a power machine having an engine compartment and a heat exchanger compartment, comprising: a fan housing located between the heat exchanger compartment and the engine compartment; a fan assembly positioned within the fan housing, the fan assembly including a center shaft with an axial fan and a radial fan coupled thereto and wherein the fan assembly has a longitudinal axis that extends lengthwise through the center shaft; a fan drive mechanism operably coupled to the fan assembly and configured to cause the fan assembly to rotate about the longitudinal axis in a first direction and a second direction; and a controller operably coupled to the fan drive mechanism and configured to provide a first control signal to the fan drive mechanism to cause the fan drive mechanism to rotate in the first direction and a second control signal to the fan drive mechanism to cause the fan drive mechanism to rotate in the second direction.
 2. The heat exchange system of claim 1, wherein the controller is configured to receive at least one input signal and wherein the controller provides one of the first and second control signals to the fan drive mechanism based on the at least one input signal.
 3. The heat exchange system of claim 2, wherein the at least one signal is indicative of temperature.
 4. The heat exchange system of claim 2, wherein the at least one input signal is indicative of the status of a fan override device.
 5. The heat exchange system of claim 1, wherein the fan drive mechanism includes: a bi-directional motor having an output shaft coupled to the fan assembly; and a directional control device coupled to the bi-directional motor and configured to cause the output shaft of the bi-directional motor to rotate in the first direction in response to the first control signal and to rotate in the second direction in response to the second control signal.
 6. The heat exchange system of claim 5, wherein the bi-directional motor is a hydraulic motor and wherein the directional control device supplies hydraulic oil to the bi-directional motor in response to the first and second control signals.
 7. A power machine having a engine located in an engine compartment and a heat exchanger located in a heat exchanger compartment, the power machine comprising: a fan housing having a fan assembly located therein positioned between the engine compartment and the heat exchanger compartment, the fan assembly configured to be rotated in a first direction and a second direction; a sensor configured to provide a sensor signal indicative of an operational condition; a fan override device capable of being manipulated by the operator and configured to provide an override signal indicative of the status of the fan override device; and a controller operably coupled to the fan assembly and configured to receive the sensor signal and the fan override signal wherein the controller is further configured to control rotation of the fan assembly based on the sensor signal and the operator signal.
 8. The power machine of claim 7, wherein the controller is configured to control the rate of speed of the rotation of the fan assembly.
 9. The power machine of claim 7, wherein the controller is configured to cause the fan assembly to rotate in the first direction based on the sensor signal.
 10. The power machine of claim 7, wherein the controller is configured to cause the fan assembly to rotate in the second direction based on the sensor signal.
 11. The power machine of claim 10, wherein the controller is configured to cause the fan assembly to change the direction of rotation from the second direction to the first direction after a pre-determined amount of time has elapsed.
 12. The power machine of claim 7, wherein the controller is configured to cause the fan assembly to rotate in one of the first direction and the second direction based on the fan override signal.
 13. The power machine of claim 7, wherein the controller is configured to cause the fan assembly to rotate in one of the first direction and the second direction based on the fan override signal, and wherein the fan override signal overrides the sensor signal.
 14. A method of exchanging heat in a power machine, comprising: providing a fan housing between an engine compartment and a heat exchanger compartment having a fan assembly with an axial fan operably coupled to a radial fan capable of being rotated in two different directions located therein; receiving a first signal indicative of a status of a fan override input; receiving a second signal indicative of a status of an operating condition of the power machine; and controlling the direction of rotation of the fan assembly in response to the first and second signals.
 15. The method of claim 14, wherein the step of controlling the direction of rotation of the fan assembly comprises: causing the fan assembly to draw air into the fan housing from the heat exchanger and the engine compartment.
 16. The method of claim 14, wherein the step of controlling the direction of rotation of the fan assembly comprises: causing the fan assembly to force air from the fan housing into the heat exchanger and the engine compartment.
 17. The method of claim 16, wherein the step of causing the fan assembly to force air from the fan housing into the heat exchanger and the engine compartment is performed in response to the second signal.
 18. The method of claim 16, wherein the step of causing the fan assembly to force air from the fan housing into the heat exchanger and the engine compartment is performed in response to the first signal.
 19. The method of claim 14, wherein the step of controlling the direction of rotation of the fan assembly comprises: causing the fan assembly to force air from the fan housing into the heat exchanger and the engine compartment; and after a predetermined amount of time, causing the fan assembly to draw air into the fan housing from the heat exchanger and the engine compartment.
 20. The method of claim 14, and further comprising: controlling the rate of speed of rotation of the fan assembly. 